Process for removing acid components from hydrocarbon solutions



March 7, 1939.

ml 2 .U .L O s N O B R A C O R D Y H M O R. F S T N E N O. P M O C D I CA G N I .V O M E R R 0 F s S E C O R nr D. L. YABROFF ET AL Filed Marchl5, 1938 .E /4 w... M ^///m //A m w, w WW Mols. KOH in solufon PatentedMar. 7, 1939 UNITED STATES PROCESS FOR REMOVING ACID COMPO- NENTSFROM-HYDROCARBON SOLUTIONS Davia Louis Yabrofr, Berkeley, and Ellis n.White,

Albany, Calif., assigncrs to Company, San Francisco,

v of Delaware Shell Development Calif., a corporation Application March15, 1938, Serial No. 196,002

Claims. This application is a continuation-impart of our co-pendingapplication Serial No. 118,920,

ledJanuary 2, 1937, and deals with the removal of weakly acid reactingorganic substances from solutions in certain organic liquids which aresubstantially immiscible with water, by extraction with aqueoussolutions of caustic alkali containing solubility promoters for thesesubstances. More particularly our invention deals with the removal ofmercaptans from hydrocarbon distillates.

It isfrequently necessary to eliminate small quantities of organicrelatively Weak acid reacting components such as mercaptans, phenols,thiophenols, etc., from their solutions in neutral or weakly basicreacting organic liquids, which are substantially immiscible with water,such as the liquid hydrocarbons derived from petroleum,

benzene, toluene, xylene, substituted normally liquid hydrocarbons whichare substantially insoluble in water, for instance, chlorinatedhydrocarbons, of which chlorpropane, chlorbutylene,

chlorbenzene, brombenzene, are examples; or

vnitrohydrocarbons, for example, nitroethane,

i nitrobenzene; or other nitrogen containing hy-A drocarbons such asamyl or higher amines, aniline, water insoluble pyridine derivatives,petroleum bases, etc. In order that the water insoluble organic liquidsmay be treated by our process they must be substantially inert andresistant to chemical reaction with strong aqueous solutions of causticalkali when contacted therewith for short periods of time, e. g., about10 minutes or less at normal room temperatures;

It isknown that weak organic acids which are little soluble in water, i.e., substantially less thanabout 1% if partly soluble are easily saltedout, and which have dissociation constants below those of fatty acids,i. e., below about 10-5 are diiiicult to extract from their solutions inwater immiscible lorganic liquids by. means 4of aqueous solutions A* ofcaustic alkali.

Itis the object of this. invention to provide a method whereby acidreacting organic substances of the type hereinbefore described can beremoved efficiently and at low cost from solutions in organicwater'immiscible liquids. As a particular application, it is the objectto remove mercaptans from strongly sour 4gasoline distillates to reducetheir sulfur content and to prof duce sweet or nearly sweet gasolines ofimproved octane numbers and lead susceptibilities. requiring littleafterv treatment for complete sweeten ing, if any. lOrganic lacidshaving dissociation constants greater than about 10-5 are in generalextractable from organic solvents by strong aqueous solutions of alkalimetal hydroxides with fair degrees of .efciency, the emciency normallyimproving with increasing dissociation constants I-frorn 3 to 5 atnormal I'OOm temperatur, 0I.

'result in operating dimculties, due,

. invention.

. has in of the acids. Therefore our improved method is .especiallyuseful in connection with the extraction of very weak acids havingdissociation constants substantially below about 10-5, although Isolution of a caustic alkali which contains dis- -IO solved and addedamount of a potassium salt of a fatty acid having from 1 to 6 carbonatoms, under conditions to absorb at least a major portion of the acidsin the aqueous solution and to form two layers, and separating thelayers.

In our co-pending application Serial No. 118,920, filed January 2, 1937,We have disclosed that alkali metal salts of fatty acids having carbonatoms promote the solvent power for weak organic acids of aqueoussolutions of caustic alkali in which these salts are dissolved. Now wehave found that potassium formate, acetate, and caproate, when dissolvedin aqueous solutions of caustic alkali also possess considerable solventenhancing properties for the weak organic acids in said aqueoussolutions, in contrast to the corresponding sodium salts which for allpractical purposes are useless, the formate even being detrimental.

'Ihe effectiveness of various salts in the matter of solubilitypromoting depends .primarily on two factors: concentration ofthesalt'limited by the solubility in the aqueous caustic alkalisolution; and specific. solubility promoting effect of the acid radicalof the salt. The higher the concentration of a given solubility promoterin the caustic alkali solution, the greater is'the solvent power ofthe-latter` for the weak organic 'acids to be extracted, andconsequently it is desirable to incorporate into the caustic alkalisolution the maximum amount of the solubility promoting salt which canbe dissolved and which will not for instance, to deposition of solids atsome point of the extraction system, of the salt solution. Thus it isfrequently advantageous -to use caustic alkali solutions which aresubstantially saturated with the salts of our Therefore they aqueoussolutions of caustic alkali are preferably about 30 to 95% saturated atnormal room temperatures with the saltsof our invention. Saturation ofabout 85% general proven to be very useful and practical in large scaleoperation.

' The specific solubility promoting eiTect gener# ally .increases withincreasing size of the organicA radical of the solubility promotingsalt.;

or to excessively high viscositiessiderable influence.

2 sing favorable specific solubility promoting powers for the organicacids are themselves insumciently soluble in strong aqueous causticalkali solutions to be of practical value. Moreover fatty acids of morethan 7 carbon atoms such as those having from 10 to 20 carbon atoms tendto create stubborn ,emulsions betweenthe aqueous and containing the sameamounts of the same causweaker bases whose alkalinitles are suicient,-

tic alkali and the same mol concentration of potassium and sodium salts,respectively, of one of the fatty acids of our invention, the solutioncontaining the potassium salt is by far the better solvent.

Due to irregularities in the solubilities with changes in the organicradicals of the fatty acid salts in aqueous solutions of caustic alkali,solvent powers of aqueous solutions saturated to the same degree ,withdifferent salts, vary between wide limits. This is demonstrated in thetable below in which the K value for n-amyl mercaptans betweeniso-octane and 5N aqueous sodium hydroxide solutions saturated withdifferent salts are given, K being concentration of, mercaptans inaqueous phase concentration of mercaptans in organic phase K value atv20C Salt Sodium Potassium Formatel .5 i0 Acetate-... 1. 3 16Propionate. l5. 5 n-Bu te 16 35 Isobutyrate.- 210 n-Valerate 8 14n-Qaproate 4. 5 9. 2

The K value for the 5N sodium hydroxide in L the absence of solubilitypromoters under the above conditions is 1.0.

WhenA dissolved in potassium hydroxide, the potassiumA salts of ourinvention are still more effective, as may be seen from the table below,in

which the K values are given for n-amyl mercaptan between 6N KOHsaturated with the salts and iso-octane.

Potassium salt K v ue at 20 C Nono 1.36 Formate mi Acetate .125Propionate'. 108 n-Butyrate. Isobutyrnie 555 n-Valerate B4 Aqueoussolutions of various caustic alkalis may however, to form in aqueoussolution substantial amounts of salts `with the organic acids havingdissociation constants below 10-5, may also be tripotssiurn phosphate,quaternary ammonium bases, etc., Fattyacid salts themselves are in,-suicientiy alkaline for this purpose, the weak acids to be extractedbeing substantially incapable of displacing the much stronger fattyacids from their salts. In other words the alkalinity of the causticalkali must be greater than that of the solubility promoting salt.

The extraction powers of the aqueous solutions vary a great deal withthe concentration not only 0f the fatty acid salts but of the causticalkali as well. This condition is illustrated in the attached drawing inwhich is plotted percent mercaptan removed from a gasoline by extractingsame with 10% by volume of aqueous potassium hydroxide, againstconcentration of the hydroxide solution vfor different amounts ofpotassium isobutyrate contained therein. As will be noted the presenceof a relatively small amount of the solubility promoter in a strongcaustic alkali solution has a considerable effect, whereas in a weakercaustic 1 alkali' solution a much larger amount of the same solubilitypromoting salt is required to exert a similar effect. `For exampleaccording to the drawing, 1.5N and 6N aqueous solutions of potassiumhydroxide remove about 12% of the mer- According to the above theconcentration of the e solubility promoter required to show a pronouncedimprovement in the extraction varies with the concentration of thecaustic alkali. While we have foundno denite rule applying to allconditions by which minimum practical amounts of f solubility promoterscan be determined without making a series of tests, it may be saidthatthe amount in mols per liter of solubility promoter should not be lessthan about 2 divided by the number of carbon atoms in the promoter salt,and furthermore the sum of the caustic alkali and solubility promoter inthe solution should be at lleast 4 mols per liter.

A point ofv interest indicated in the drawing is that the combinedveiiects of the caustic alkali and solubility promoter are far greaterthan the sum of their individual eil'ects. The following examples serveto illustrate this point more clearly:

Three samples Voi' iso-octane containing dissolved n-amyl vmercaptanwere shaken with the followingA three aqueous solutions, and thedistribution constants K for the mercaptans between the iso-octane' andthe solutions were determined:

Percetnt mer cap au ex- Solution in water glug tracted with 10% by vol.

aqueous phase 3.09N potassium iosbutyrate .0005 '0. 0l 6N KOH 1.36 l1.97 3.09N potassium iosbutyrate-I-SN KOH. 384 97. 4

The amounts of aqueousv caustic alkali solution containing solubilitypromoter employed in thev extraction are normally above volume percentand for economic reasons seldom exceed 100 volurne percent. Wh'enextracting mercaptans from hydrocarbon distillates with potassiumhydroxide containing potassium isobutyrate for the purpose ofsweetening, normally about to 50 volume percent are employed -dependingupon the boiling l range of the hydrocarbon, the type of mercaptanscontained therein and the number of extraction stages.

Although the'solubiliti'es of the fatty acid salts in the aqueoussolutions of caustic alkali increase with 'increasing temperatures, theapplication of elevated temperatures for extraction offers few, if any,advantages, because the extraction power of a given caustic alkalisolution containing promoter salt, for the weak acids decreases withincreasing temperatures. Therefore we usually prefer to operate attemperatures between about 0 to 60 C. I

Spent caustic alkali solutions containing the salts of this invention,used in the extraction of mercaptans from solutions in organic waterinsoluble liquids, can be regenerated readily and efciently by steamingas described in our co- 'pending application Serial No. 174,512, led

November 15, 1937.

'Ihe following examples serve furtherto 'illustrate our plocess. f

t Example I A Acracked distillate known to contain alkyl phenols wasextracted with'5% by volume 40 B. KOH and 6N KOH containing" 3.0 molpotassium isobutyrate per liter, respectively. To determine the relativealkylphenol contents in the extracts so obtained, 5 ml. samples of theextracts were acidifled and washed with 125ml. of a reformedunstablegasoline having an induction period of minutes. The liberatedalkyl phenols were dissolved in thel washed gasolines which were thendiluted with'9 times their own volume of the fresh reformed gasoline.The induction perlods of the resulting mixtures were then determined.They served-.as a, relative measure of the l amount of alkyl phenolscontained in the extract samples and also for the relative extractionefficiency of thetwo extractants. Results wereas Assuming that theinduction period is a straight line function of the amount of alkyl -perliter potassium valerate, respectively.

Astantially insoluble in of an alkali metal hydroxide in phenols added',an .assumption which is essentially correct, it will be seen that the 40B. KOH solution extracted only 60% of the alkyl phenols extracted by theKOH solution containing potassium isobutyrate. It is of interest to notethat analytical methods heretofore in use for the determination of alkylphenols in hydrocarbon oils were based on the assumption that 40 B. KOHor NaOH is capable of extracting all the alkyl phenols` contained inhydrocarbon oils. Obviously by using in the analytical method KOHsubstantially saturated with potassium isobutyr- ,t atc results areobtained which givea much truer picture of the actual content of thealkyl phenols.

l Example III A sour light gasoline boiling below 100 C. and containingessentially methyl and ethyl mercaptans was sweetened by extraction inseveral stages withV 6N KOH solution substantially saturated withpotassium acetate. The use of the acetate in the treatment of thisparticular gasoline was more economical than the use of the isobutyrate,because the former requires considerably less steam for regenerationthan the latter.

Example IV Two samples of benzene containing .0272 inols per literthiocresol were extracted with 10 volume percent each of 14% aqueousammonia and 14% aqueous 4ammonia containing dissolved 400 gm. The

amounts of thiocresol extracted were 46% and 69%, respectively.

. We claim as our invention:

1. In a process of separating organic acids sub"- water and havingdissociation constants below about 10-5 from an organic water-insolubleliquid in which they are dissolved and which is substantially inerttoward aqueous V strong bases under the conditions ofthe process,

by extraction with an aqueous solution of a strong base, the improvementcomprising extracting said organic liquid with an aqueous solution of astrong base containing dissolved a substantial amount of a potassiumsalt of a fatty acid having from 1 to 6 carbon atoms per molecule, the

alkalinity ofthe solution being in excess of that of-said potassiumsalt, under conditions to absorb at least aportion of said organic acidsin said aqueous solution and to form two liquid layers, one comprisingthe aqueous solution containing absorbed organic acids, and the otherconsisting essentially of the organic liquid, and separating the layers.

2. The process of daim 1 inwhich the strong base isl at least 30%saturated at normal room temperature with the fatty acid salt.

3. In a process of separating organic acids substantially insoluble inwater and-having dissociation constants below about 10- from an organicwater-insoluble liquid in which they are dissolved and which issubstantially inert toward aqueous strong bases under'the conditions ofthe process, by extraction with an aqueous solution of a strong base,the improvement comprisingxtracting said organic liquid with anaqueousfolution which is lissblved a substantial amount of a potassiumsalt gf a fatty acid having from 1 to 6 carbon atoms per molecule, underconditions to absorb atleast a portion of said organic acids in saidaqueous solution and to form two liquid layers, one comprisi 1g theaqueous solution containing absorbed organic acids, and the otherconsisting essentially of the organic liquid, and separating the layers.y

4. The process of claim 3 in which the alkali metal hydroxide ispotassium hydroxide. l

5. The process of claim 3 in which the alkali metal hydroxide is between1 to 10 normal.

-6. The process of claim 3 in which the alkali metal hydroxide solutioncontains an amount of fatty acid salt in mols per liter equal to atleast 2 divided by the number of carbon atoms in the salt, and in whichthe sum of alkali metal hydroxide and fatty acid salt is at least 4 molsper liter.

7. In the process of separating mercaptans from a hydrocarbon liquidcontaining same, by extraction with an aqueous solution of a causticalkali, the improvement comprising extracting said hydrocarbon liquidwith an aqueous 1 to,10

normal solution of an alkali metal hydroxide inl which is dissolved apotassium `fatty acid salt having from 1 to 6 carbon atoms per moleculein an amount in mols per liter equal to at least 2 divided by the numberof carbon atoms in the salt, and in which the sum of alkali metalhydroxide4 and fatty acid salt is at least 4 mols per liter, underconditions to absorb at least a major portion of the mercaptans in thehydroxide solution and to form two layers, one comprising an aqueousalkali metal hydroxide solution containing the potassium fatty acid saltand mercaptides and the other consisting essentially of the hydrocarbonliquid, and separating the layers.

8. In the process of separating mercaptans from a hydrocarbonliquidcontaining same, by extraction with an aqueous solution of causticalkali, the improvement comprising extracting said hydrocarbon liquidwith a 1 to 10 normal aqueous solution of an alkali metal hydroxidewhich is 30 to 95% saturated atl normal room separating the layers.

temperature with potassium isobutyrate, under conditions to absorb atleast a major portion of theA mercaptans in the hydroxide solution andto form two layers, one comprising an aqueous alkali metal hydroxidesolution containing the potassium fatty acid salt and mercaptides andthe other consisting essentially of the hydrocarbon liquid, andseparating the layers.

9. In the process of separatingmethyl and ethyl mercaptans from ahydrocarbon liquid containing the same, by extraction with an aqueoussolution of caustic alkali, the improvement comprising extracting saidhydrocarbon liquid with a 1 to 10 normalaqueous solution of an alkalimetal hydroxide which is 30 to'95% saturated at normal room temperaturewith potassium acetate, under conditions-to absorb at least a majorportion of the mercaptans in the hydroxide solution and to form twolayers, one comprising an aqueous alkali metal hydroxide solutioncontaining the potassium fatty acid salt and mercaptides and the otherconsisting essentially of the hydrocarbon liquid, and

l 10. In the process of sweetening a sour hydrocarbon distillate byextracting same with an aqueous solution of a caustic alkali, theimprovement comprising. extracting said distillate in a countercurrentextractor of at least three stages with 10 to 50 volume percent of a 2to 10 normal potassium hydroxide solution which is about saturated atnormal room temperature with potassium isobutyrate, under conditions toform two layers, one comprising an aqueous solution of potassiumhydroxide containing the'visobutyrate and mercaptides, and the otherconsisting of ad sweetened hydrocarbon distillate, and separating thelayers.

DAVTD LOUIS YABROFF.

EimsawHrI'E.

